In off-shore drilling environments, it is necessary to supply chemicals such as methanol or glycol to the wellhead and this is achieved using flexible hoses or multi-conduit hoses, sometimes referred to as umbilicals. Such umbilicals may be from 50 m in length to well in excess of 100 km in length in use in the field. In a multi-conduit hose or umbilical, each of the flexible hoses therein may be used for transporting different types of chemical, eg, one for transporting methanol and one for glycol and others for transporting other hydro-carbon gases. Additionally, in an umbilical there may be other lines such as hydraulic control lines, injection lines and/or service lines, eg, electrical conductors and fibre optic cabling. The present invention relates also to so called “High Collapse Resistant Hoses” of the type used in deep sea applications, which, in use, must be able to resist collapsing due to the very large pressures exerted thereon.
United Kingdom Patent Publication No. GB2245678A discloses an umbilical for use in the transportation of the aforesaid chemicals, eg, methanol and glycol. A particular disadvantage that has been identified with hoses generally and in particular the umbilical, and hoses, disclosed in the aforesaid publication is that they are permeable, to a greater or lesser extent, to chemicals with small molecular sizes/molecular shapes, as those found in methanol, ethanol and other hydro-carbon gases. Nylon material has been used for many years in conduits and Nylon 11 in particular has good physical stability except that it has poor permeation characteristics. Over long lengths, typically several kilometres, GB2245678A utilises materials which have slightly improved permeation characteristics but such an arrangement is not wholly acceptable to the offshore industry from an emissions perspective and lack the physical stability of materials such as Nylon 11. Furthermore it will be appreciated that over very long lengths material costs are a significant factor to be considered.
Additionally, it has been found that it is possible for there to be cross contamination between adjacent hoses within an umbilical wherein chemicals transported through one hose permeate out of that hose into an adjacent hose which may contain a different chemical.
Conduits and umbilicals for the transportation of various fluids are described variously in EP 1020673, JP 2000-002375, U.S. Pat. No. 4,570,680, GB 838070 & GB 699543.
Another issue in conduits/umbilicals of a one piece construction and very long length, typically in excess of 100 km, is that permeation is acceptable, where the conduit/umbilical is, for example, under water, but permeation is to be avoided where the umbilical surfaces, top side, or when the conduit/umbilical passes across ground because of the hazardous/flammable nature of some permeable fluids. Umbilicals having a plurality of different fluid conduits having differing permeation characteristics along a given length have not previously been proposed.
Moreover hoses for umbilicals are generally produced in very long lengths e.g. 100 km or more and are required to have a combination of features to make them suitable for subsea use e.g. high temperature resistance, high chemical resistance and low permeation rates. Some flouropolymers are particularly suitable for this application but production of conduits in the aforesaid extremely long lengths is not possible due to oligomer and low molecular species building up on extrusion tools and damaging the liner/conduit after a short while.
It is an object of the present invention to avoid or minimise one or more of the aforesaid problems.